An ultra-high yield of spherical K2NaScF6:Mn4+ red phosphor and its application in ultra-wide color gamut liquid crystal displays

Mn4+-Activated narrow-band red-emitting fluoride phosphors are an efficient red compensator able to widen the color gamut and improve the color quality of pc-WLEDs for backlight display applications. However, the low synthetic yields and extremely non-uniform, irregular morphologies of these fluorides seriously restrict their practical industrial applications. Herein, a novel Mn4+-doped narrow-band redemitting phosphor K2NaScF6:Mn4+ was prepared through a simple co-precipitation route. High-resolution synchrotron XRD and its Rietveld refinement reveal that K2NaScF6:Mn4+ crystallized in the space group Fm3m with a cubic structure and that the octahedral Sc3+ sites were occupied by Mn4+, resulting in a very small amount of alkali metal cation vacancies for charge compensation. The electronic band gap of K2NaScF6 was calculated to be 6.46 eV by DFT calculations, which ensured the location of Mn4+ energy levels in the host band gap and was verified by DRS results. Unlike previously reported Mn4+-activated fluorides, K2NaScF6:Mn4+ has an ultra-high synthetic yield (B100%) and a uniform spherical morphology with extremely narrow size distribution (similar to 1.17 mu m). Excess KHF2 and the extremely low solubility of K2NaScF6 were shown to be responsible for the high synthetic yield of K2NaScF6:Mn4+. Under blue light illumination, K2NaScF6:Mn4+ exhibited an intense sharp-line red fluorescence peak at 630 nm. Meanwhile, the ZPL intensity could be tailored through the control of Mn4+ amount in the K2NaScF6 matrix. By employing the efficient and stable K2NaScF6:Mn4+ as an efficient red emitter, two pc-WLEDs with ultrawide color gamut (Rec. 2020 value of 95.1% and NTSC value of 127.3% for LED-1, Rec. 2020 value of 96.7% and NTSC value of 129.5% for LED-2) were successfully obtained. These results suggest the great potential of K2NaScF6:Mn4+ as a red-emitting phosphor for applications in high-quality backlight displays, and this work may open a perspective for researchers to design new luminescence materials with high synthetic yield and uniform spherical morphology.